The present invention relates to an improved process for producing a silicone composition useful as a green tire lubricant, and more particularly, the present invention relates to an improved process for preparing a green tire lubricant with improved lubricity properties wherein the improvement comprises mixing the polydiorganosiloxanes with the mica filler initially to form a homogeneous mixture before the other necessary and optional ingredients are added.
Lubricants for green tire bladders are well-known. See, for instance, the patent application of Frank J. Traver, Ser. No. 534,101, filed Dec. 19. 1974, entitled WATER BASED GREEN TIRE LUBRICANTS and the prior art cited in that application.
In the manufacture and vulcanization of tires, the green tire mass, which is in the form of a cylinder, is placed in the mold and as the mold closes, the bladder, or bag as it is known in the industry, is inflated by means of air pressure or hot water inside the tire. This inflation forms the tire into the shape of the mold. It has become necessary in this manufacturing procedure of tires, to apply a lubricant to the inside of that green tire mass, one such that the bladder will have the appropriate static friction to apply pressure for the formation of the tire and also so that the bladder will have some slipping properties so that it will not rupture.
Early in such manufacturing procedures organic lubricants were utilized but it was found that such organic lubricants lacked the proper lubricity properties, that is, such lubricants did not have the combination of static friction to sliding friction which was necessary for a particular green tire mass design. It was found that silicone lubricants were, in certain cases, more desirable in the lubrication of bladders for the formation of vulcanized tires from green tire masses. Accordingly, one example of such silicone green tire lubricants is found in the foregoing Traver patent application.
Silicone lubricating compositions, while having many advantages in terms of lubricity properties and high temperature stability, nevertheless, did not always present the optimum lubricity properties for the bladder in the vulcanization of the green tire mass to form vulcanized tires.
Accordingly, it was found for many green tire designs that the silicone lubricant composition that was most desirable was one where the static friction was a tenth of a point larger than the sliding friction as determined by lubricating methods and where the static friction was at least 0.4. Such a combination of static to sliding friction was often obtained by merely varying the amount of filler or the amount of silicone polymer that was utilized in the composition or the variation of other ingredients to get the appropriate combination of static to sliding friction. Unfortunately, however, the resulting lubricant even though having the desired static to sliding friction combination would in many cases, as a result of the excessive loadings of filler, precipatate such filler out of the lubricant composition into the inner part of the tire and as a result the lubricant would lose its effectiveness. Accordingly, in such cases unless the silicone lubricant was continually applied to the bladder after the vulcanization of each tire there would result a rupture of the bladder.
It should also be pointed out that in such silicone green tire lubricant compositions, it was highly desirable to have mica as a filler. Mica is desirable as a filler in such green tire lubricant compositions since it imparts to the lubricant the proper balance of allowing the lubricant to breathe, that is, to allow air to pass there through during the vulcanization process of the tire thus not creating air pockets in the inward side of the tire mass.
Accordingly, in such silicone green tire lubricant compositions, it was found necessary, that most of the filler be a mica filler, although to a certain extent minor amounts of other fillers could be utilized in combination with the mica filler. In addition, the practice, as can be seen from pages 11 and 12 of the foregoing Traver application, was to first form a dispersion of the polysiloxane polymer with the emulsifying agents in water before the filler and other additives were added to form the desired composition. It was felt at that time that a proper dispersion could not be made unless the water and polysiloxane polymer and emulsifying agents were first added to form the silicone emulsion before the other ingredients were added. Unfortunately, it was found by such a process for producing such green tire lubricants as that set forth in the foregoing Traver case that the optimum lubricity properties were still not obtained with respect to the correlation of static to sliding friction. Although the mica was present in the composition and did allow the silicone lubricant composition to escape air, nevertheless, the silicone polymer in the composition did not lubricate the mica composition sufficiently so that the lubricant did not have the proper mixture of static to sliding friction unless the amount of silicone polymer and mica, as well as other ingredients, were unduly mixed resulting in the problems mentioned previously. With such a procedure of preparing the silicone green tire lubricant, as that disclosed in the foregoing Traver case, it was difficult if not impossible in some cases to obtain the optimum lubricity properties, that is, the combination of static to sliding friction for a particular designed green tire mass.
In addition it was found that with the prior art method of preparing the silicone lubricant, the mica in many cases, after repeated use of the bladder bag, would precipitate out and cause the lubricant to malfunction.
Accordingly, it was found to be highly desirable to have a process in which to properly lubricate the mica filler in preparing the green tire lubricant, such that the resulting green tire lubricant composition would not have the foregoing disadvantages.
Another problem that was obtained with utilization of prior art silicone green tire lubricant, was that as mentioned previously, it was necessary basically to have a certain filler loading as well as the other additives mentioned above to give the green tire silicone lubricant the proper balance of static to sliding friction for a particular green tire mass as well as a static friction that was high enough. However, unfortunately, there resulted in such composition as a result of unduly high filler loadings an undue increase in the viscosity of the final silicone green tire lubricant composition. Accordingly, for many machines and molding equipment that utilize silicone green tire lubricants it was found that lower viscosities were desired in the composition to be utilized in the molding equipment for spraying the silicone lubricant on the bladder. It was also highly desirable from a manufacturing point of view for producing silicone green tire lubricants that a particular manufacturer of tires specified a certain viscosity for the green tire lubricant and a certain static to sliding friction for that manufacturer of such green tire silicone lubricant to be able to control from batch to batch the final viscosity of his material.
Accordingly, it was highly desirable to find a simple process which would be utilized to monitor the viscosity of the silicone green tire lubricants to a constant value from batch to batch without such methods affecting other necessary properties of the silicone green tire lubricant composition and specifically the values of static and sliding friction.
Accordingly, it is one object of the present invention to provide for an improved process which allows an optimum lubrication of a mica filler in the production of a silicone green tire lubricant composition such that the final composition has the proper balance of static to sliding friction and a static friction that is at least 0.4. An additional object of the present invention is to provide for an improved process for producing a silicone green tire lubricant where a stable dispersion of the lubricant composition is formed while obtaining an optimum lubrication of the mica filler with the polysiloxane polymer.
It is an additional object of the present invention to provide for an improved process for controlling the end viscosity of a silicone green tire lubricant composition with little effect on the ingredients utilized in preparing the green tire lubricant composition.
It is still an additional object of the present invention to provide for an improved process in producing a silicone green tire lubricant composition which the viscosity of the composition can be controlled from batch to batch while still maintaining an optimum combination of static to sliding friction in the composition.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.